The following proposal deals with identification and analysis of genes important to early development. These genes map to a chromosomal segment in the genome of Drosophila melanogaster which is previously shown to be essential to nervous system formation. To identify those loci that affect neurogenesis: 1) the chromosomal segment will be saturated with lethals and temperature sensitive conditional lethals; 2) lethal complementation groups will be defined; 3) the loci represented by embryonic lethal alleles will be identified; 4) the embryonic phenotype of the lethal embryos will be characterized. To understand normal functions provided by these genes and the tissue specificity of the gene action a thorough developmental genetic analysis will be done. The developmental-genetic analysis will entail: 1) description of nervous system formation at a morphological level; 2) use of conditional alleles - a. to determine time of gene action and b. study the effect of mutation on embryonic as well as postembryonic development; 3) use of genetic mosaics (somatic recombination mosaics and gynandromorphs) - a. determine if the lethal mutation is "cell viable", b. to map the lethal focus", c. to characterize the the nervous system in genetic mosaics, and d. to study the effect of the mutation on the cuticular and sensory neural tissues, e. to study interaction between mutant and non-mutant tissues juxtaposed in a developing organism. The proposed analysis will aid to the genetic ideas on genome organization of closely linked loci with related developmental functions. It will help define genes necessary for neurogenesis and the characterization of the mutant alleles of these genes will provide insights into functions necessary for nervous system formation. Genetic variants in genes that act specifically in neural development will add to the tools available to manipulate neural development.